Microstructure and kinetics evolution in MgH2-TiO2 pellets after hydrogen cycling

The interest in Mg-based hydrides for solid state hydrogen storage is associated to their capability to reversibly absorb and desorb large amounts of hydrogen. In this work MgH2 powder with 5 wt.% TiO2 was ball milled for 10 h. The as-milled nanostructured powder was enriched with 5 wt.% of Expanded Natural Graphite (ENG) and then compacted in cylindrical pellets by cold pressing using different loads. Both the powder and the pellets were subjected to kinetic and thermodynamic tests using a Sievert's type gas reaction controller, in order to study the microstructural and kinetic changes which took place during repeated H-2 absorption and desorption cycles. The pellets exhibited good kinetic performance and durability, even if the pressure of compaction revealed to be an important parameter for their mechanical stability. Scanning Electron Microscopy observations of as-prepared and cycled pellets were carried out to investigate the evolution of their microstructure. In turn the phase composition before and after cycling was analyzed by X-ray diffraction. (C) 2013 Elsevier B.V. All rights reserved.